1. Field of the Invention
The present invention relates to a piezoelectric electroacoustic transducer that is suitable for surface mounting and a manufacturing method thereof, and in particular relates to a structure of terminals thereof.
2. Description of the Related Art
In electronic devices, electronic home appliances, portable telephones, and other such electronic devices, piezoelectric electroacoustic transducers have been widely used as a piezoelectric buzzer or piezoelectric receiver for producing an alarm sound or an operating sound. A piezoelectric electroacoustic transducer of this type generally includes a circular piezoelectric element bonded to one surface of a circular metallic plate to form a unimorph-type diaphragm, and the periphery of the metallic plate is mounted on a circular case using silicone rubber while an opening of the case is closed with a cover.
However, when using a circular diaphragm, there has been a problem of low production efficiency, low acoustic conversion efficiency, and moreover, difficulty in miniaturizing the piezoelectric electroacoustic transducer.
A piezoelectric electroacoustic transducer is described in Japanese Unexamined Patent Application Publication No. 2000-310990 as improving production efficiency and acoustic conversion efficiency, and can be miniaturized by using a rectangular diaphragm. The piezoelectric electroacoustic transducer includes a rectangular piezoelectric diaphragm, an insulating case having a bottom wall, four sidewalls, and a supporting member, which is disposed inside between two of the sidewalls opposing each other for supporting the diaphragm, the supporting member being provided with first and second conductive members formed therein for external connection, and a lid plate having holes formed thereon for releasing sound. The diaphragm is accommodated within the case, where two opposite sides of the diaphragm are fixed to the supporting member with an adhesive or an elastic sealant, while gaps between the remaining two sides of the diaphragm and the case are sealed with the elastic sealant, so that the diaphragm and the first and second conductive parts are electrically connected together with a conductive adhesive, and the lid plate is bonded on the open end of the sidewalls of the case.
The above-mentioned Publication, as shown in FIGS. 12 to 15 of the Publication, discloses a method for fixing the terminal to the case such that the terminal is insert-molded along the bottom surface of the case in advance, and then, the end portion of the terminal is bent upwardly along the side wall of the longer side of the case. In this case, it may be difficult to insert-mold because of the complexity of the terminal configuration and it may be difficult to form a fillet for soldering because of a small area of the terminal exposed on the side surface of the case.
The terminal is formed substantially straight during insert molding, and after the insert molding, an external connection protruding from the case is bent toward the bottom surface of the case via the side surface thereof so as to be able to form a terminal suitable for surface mounting. This structure has an advantage that a fillet for soldering is readily formed, because the shape of the terminal is simple and furthermore the external connection of the terminal is bent toward the bottom surface via the side surface.
However, in the structure described above, since the internal connection of the terminal is exposed in the supporting member of the case while the external connection is protruded outside the case, when bending the external connection toward the bottom surface via the side surface, the bending stress spreads also toward the internal connection, so that a loose part may be produced in the internal connection. Therefore, when connecting the diaphragm onto the internal connection, there may be a problem that the diaphragm is not stabilized so that sound pressure characteristics are degraded.
For the terminal, a pressed terminal punched from a metallic plate is generally used, wherein a flash is inevitably produced so that when the flash is exposed on a soldering surface of the external connection, a defect such as a loose part may be produced during mounting.